The present invention relates to a process for producing the field oxide of an integrated circuit. It more particularly applies to the production of MOS integrated circuits.
One of the main process for producing the field oxide is generally called the "LOCOS Process" and the different stages thereof are shown in FIGS. 1 to 4.
As shown in FIG. 1, the first stage of this process consists of thermally growing on a silicon substrate 2, e.g. type P silicon, a silicon oxide layer 4 of limited thickness, i.e. approximately 0.07 microns, then depositing a silicon nitride layer 6 on oxide layer 4 and which generally has a thickness of approximately 0.08 microns. After producing a resin mask 8 on region 6a of silicon nitride layer 6, positined above the substrate region in which is subsequently produced the elementary component of the integrated circuit, e.g. the central region of the silicon nitride layer of FIG. 1, the silicon nitride layer 6 is etched, e.g. by plasma etching or attack. The thus obtained structure is shown in FIG. 2.
After etching the silicon nitride layer 6, through oxide layer 4, are implanted ions giving doping of the same type as that of the substrate. In substrate 2, this ion implantation makes it possible to obtain two lateral regions 10 and 12 e.g. of type P+ in the case of a type P substrate and an implantation of boron ions. This implantation takes place with a dose of 2.10.sup.12 atoms/cm.sup.2 and an energy level of 140 keV for example.
The resin mask 8 is then eliminated. The following stage consists of producing the field oxide by thermal oxidation of the silicon, the active zones in which it is wished to produce the elementary components being masked by region 6a of the silicon nitride layer during said oxidation process. This leads to two lateral silica regions 14, 16 having a thickness which is generally between 0.6 and 0.8 microns.
This process is finished by eliminating region 6a of silicon nitride layer 6 and the region of oxide layer 4 positioned above the region of substrate 2 in which the component is subsequently formed. For example, this elimination takes place by a chemical attack. The thus obtained structure is shown in FIG. 4.
This process for producing the field oxide of an integrated circuit has a certain number of disadvantages.
In particular, the thermal oxidation stage for obtaining silica regions 14 and 16 is long and tedious. Thus, said thermal oxidation is carried out at a relatively low temperature of approximately 900.degree. C. for approximately 10 hours. Moreover, this prolonged heat treatment leads to a diffusion of the implanted ions into regions 10 and 12 of the substrate. This redistribution of the ions, requires implantations and relatively strong dose levels.
In addition, this process for producing the field oxide has the major disadvantage of limiting the integration density of the integrated circuits. Thus, the field oxide produced by this process has a significant lateral extension L in FIG. 4.